By way of background in xerography or an electrostatographic process, a uniform electrostatic charge is placed upon a photoreceptor surface. The charged surface is then exposed to a light image of an original to selectively dissipate the charge to form a latent electrostatic image of the original. The latent image is developed by depositing finely divided and charged particles of toner upon the photoreceptor surface. The charged toner is electrostatically attached to the latent electrostatic image areas to create a visible replica of the original. The developed image is then usually transferred from the photoreceptor surface to a final support material such as paper, and the toner image is fixed thereto to form a permanent record corresponding to the original.
In some xerographic copiers or printers, a photoreceptor surface is generally arranged to move in an endless path through the various processing stations of the xerographic process. Since the photoreceptor surface is reusable, the toner image is then transferred to a final support material, such as paper, and the surface of the photoreceptor is prepared to be used once again for the reproduction of a copy of an original. In this endless path, several xerographic related stations are traversed by the photoconductive belt.
Generally, after the transfer station, a photoconductor cleaning station is next and it comprises an endless photoconduction belt which passes sequentially to a first cleaning brush, often a second cleaning brush and after the brushes are positioned, a spots blade which is used to remove residual debris from the belt, such as toner additive and other filming. A problem is that the good cleaning efficiency of the cleaner brushes leaves a minimal amount of toner on the photoconductor and the spots blade is therefore inadequately lubricated.
One widely accepted prior art method of cleaning residual toner from the surface of a photoreceptor of a typical copier or printer is by means of a cylindrical brush or brushes rotated in contact with the photoreceptor surface at a relatively high rate of speed. Generally, rotatable brushes are mounted in interference contact to the photoreceptor surface to be cleaned, and the brushes are rotated so that the brush fibers continually wipe across the photoreceptor. Electrical bias applied to conductive brush fibers aids in removing and transporting cleaned material away from the photoreceptor surface. In order to reduce the dirt level within the brush, a flicker bar and vacuum system may be provided which removes some residual toner and toner agents from the brush fibers and exhausts some of the residual toner and toner agents from the cleaner. Alternatively, toner may be cleaned from the brush fibers by electrostatic transfer to electrically biased detoning rolls. Charged toner particles are transferred from the brush fiber tips to the detoning roll surface electrically biased to the opposite polarity of the toner charge. The toner cleaned from the cleaning blade is then removed from the detoning roll by a scraper blade. Unfortunately, the brush could become contaminated with toner and toner agents and, after extended usage, needs to be frequently replaced. Brush life is ultimately compromised by toner and additive impaction on fiber ends that affects conductivity and physical changes to brush through mechanical or electrical breakdown that affect the mechanical integrity and/or electrical conductivity. With increased processing speeds of today's copiers and printers and the expanded use of toner agents, the foregoing brush cleaning techniques are not totally effective or practical.
Electrostatic brush (ESB) cleaning has been long the choice for high volume cleaning applications. ESB cleaning provides superior reliability when compared to blade cleaning but at much higher unit manufacturing cost (UMC). Air detoning prevents the build up of toner within the brush but requires an expensive and high power usage air and filtration system to remove cleaned toner from the detoning air stream. Electrostatic detoning of ESB cleaners is lower cost than air detoning but the brushes must be periodically vacuumed or replaced to prevent print defects when toner build up within the brush falls out.
ESB cleaners are limited in their cleaning capacity by the density of fibers on the brush and photoreceptor drag and wear caused by the brush pile. Smaller brush fiber diameters allow greater fiber densities for greater cleaning capacity and can reduce the stiffness of the brush pile. There is, however, a practical limit to the reduction of brush fiber diameter. Experience has shown that brush stiffness can be reduced with very small fiber diameters, but photoreceptor wear increases when compared to larger fibers. The explanation is that electric discharges from the smaller fiber tips generate erosion of the photoreceptor surface. The minimum brush fiber diameter limitation creates an ESB cleaning capacity limit.
The present invention provides an electrostatic roll cleaner and a cleaning station whereby the roll cleaner comprises a compliant foam underlayer having a coating thereon of a conductive woven, non-woven, braided or knit fabric. The cleaning station is in electrical contact with a biasing structure. This structure is configured to bias the fabric relative to the photoreceptor ground surface from +50 to +500 volts to clean negatively charged toner and from −50 to −500 volts to clean positively charged toner.
Since most toners used today are negatively charged, the embodiments throughout this disclosure and claims will be described relating to the use of a negative polarity toner; however, when a positive polarity toner is used, the proper opposite polarity adjustments can easily be made, such as biasing of the detoning roll and biasing of the conductive fabric, as will be described below.
While the cleaner roll of this invention is described herein in reference to cleaning a photoreceptor surface, it can also be used in other xerographic stations such as a cleaner in an intermediate transfer belt, biased transfer roll, biased transfer belt, or fuser station. Similarly, the cleaner roll fabric covering of this invention is described herein as conductive. The cleaner roll fabric covering can also be non-conductive. If the cleaner roll fabric covering is non-conductive, the fabric material will be chosen to tribocharge against the contacting surfaces such that the appropriate electrical potential for cleaning and detoning is generated on the surface of the fabric. Because the cleaner roll fabric covering is non-conductive, the detoning roll surface need not be a dielectric, e.g., the anodized aluminum surface used with conductive rolls, but could be a simple conductive surface, e.g., stainless steel. Because of variations caused by environmental temperature and humidity and contamination of contacting surfaces, generation of cleaning electrical biases through tribocharging is less predictable than direct biasing of conductive fabrics with a voltage source. For these reasons direct biasing of conductive fabric electrostatic rolls is preferred.